'A masterpiece,' Tim Adams called it in this newspaper, and many people anticipate that on Tuesday, the judges will agree and award the Man Booker Prize to Alan Hollinghurst's fourth novel, The Line Of Beauty. Elegant, erudite and studded with plenty of racketty gay sex, the book takes up where Hollinghurst's first novel, The Swimming-Pool Library, left off, in the mid-1980s, and charts the high water marks of Thatcherism and Aids, and the sickness and scummy disillusionment they left behind.

The Swimming-Pool Library, which was published in 1988, was described by Edmund White as 'the best book about gay life yet written by an English author'. Exhilaratingly libidinous, full of pre-Aids pleasure, it appeared with a tremendous sense of shock. The novelist Philip Hensher was 22 when it was published and recalls its impact: 'I remember coming down from university to London to buy it as soon as possible. It was extremely important to my generation: before that, you couldn't imagine a gay novel about gay life appealing to anyone else.'

Hollinghurst followed with The Folding Star in 1994, which was also short listed for the Booker, and The Spell in 1998. He writes, he has said, 'at walking pace', a rate of 300 to 400 words a day, or perhaps none. His close friend Andrew Motion remarks: 'I sometimes ask him, "What have you been doing today?" and he says, "thinking".'

Hollinghurst was born in Stroud, Gloucestershire, in 1954 and grew up around Cirencester, where his parents - his father was a bank manager, and he was their only child - encouraged his enthusiasm for listening to music. After public school at Canford, in Dorset, Hollinghurst went to Magdalen College, Oxford. He won the Newdigate Prize for poetry the year before Andrew Motion. 'My first impressions, which got stronger as I knew him, were that he was exceptionally clever,' Motion recalls, 'with an extraordinary range of cultural knowledge. And he spoke extremely elegantly, rather as he writes, with developed periods and an unfading, steady sense of the high style.'

They subsequently shared a house for a couple of years, where Motion picked up some of his friend's knowledge of romantic music. 'It was one of the happiest times of my life,' Motion says. 'We were quite worky. He was writing a novel, which in the end he didn't offer for publication. At weekends we often went off to look at houses. We kept the National Trust going all by ourselves. And we established a pattern we've kept up since, of showing each other any work we plan to offer for publication. He has fantastically good taste and judgment. I don't know what I'd do, if not for him: if he thinks it's all right then that's good enough for me. I don't have to care what anyone else thinks.'

Motion bought The Swimming-Pool Library when he was editorial director of Chatto: 'I knew it was going to be good, but I was flabbergasted by how brilliant it was.' Hollinghurst became godfather to Motion's eldest child.

By this time, Hollinghurst was working at the Times Literary Supplement. There is a sense in his books of life opening up for young people in London, and his friends suggest that this was very much his experience, and that it accelerated following the publication of his first novel.

'Before The Swimming-Pool Library , it didn't seem to me that being Alan and being gay was particularly happy. A lot of it revolved around opera,' says Alan Jenkins of the TLS . 'After it, life became a sort of party. He had a bit of success and money, and every gay man in the world had read and admired his book. That opened up a range of possibilities that hadn't been there before.'

With his passion for Wagner, his enthusiasm for architecture and his cheerful ignorance of much popular culture (although the clubbing means he can display odd flashes of knowledge about garage) Hollinghurst can seem to be a rather austere, Olympian figure.

'His monastic routines when he's writing don't easily accommodate the scheduling of soap opera,' says Stephen Pickles, who shared the house in Oxford before Motion returned from Hull.

Hollinghurst is quite reserved: self-possessed, one friend said, without much small talk at the outset, and he has a deep, impressive voice, which can make him seem forbidding. He also knows a scary amount about literature: he used to edit Nemo's Almanac, an abstruse annual competition for literary nerds, which involves identifying obscure bits of writing, mainly by poets no one remembers.

He still does the competition, and 'he'll say things like, "seven eluded me", when I've spent three months on it and only got one,' notes Peter Strauss, who bought The Line of Beauty when he was at Picador (he is now an agent). 'And then he'll tell me that was wrong.'

Part of the pleasure of Hollinghurst's writing lies in the tension between the impeccably modulated prose and the pleasurably filthy things people get up to. It's difficult to imagine how, in life, he squares these sides of himself: the exquisitely discerning, intellectual Hollinghurst and the clubbing one. He has never gone out dancing all that often: once a month perhaps; but he has enthused about the pleasures of taking Ecstasy when he does.

It's possible that he manages by keeping the worlds entirely separate. Andrew Motion says he is 'extraordinarily compartmentalised'. Stephen Pickles says: 'I don't know about Ecstasy or clubbing. I'm not interested in those things and he doesn't talk about them, or not to me.'

The central characters of The Swimming-Pool Library and The Line of Beauty both suffer unrequited passions for handsome young contemporaries who are barely aware of their lustful fantasies.

Both books also feature urgent, exhilarating sex with working-class black men. This seems not to be a million miles away from life. 'For quite a while, he could be depended on to like boys who didn't like boys,' Alan Jenkins comments, 'and he's always liked and fancied black boys. He's had long-term affairs and he's still close to those boys. They haven't all been working class by any means: they've been heterogeneous in that sense; but they have tended to be black.'

Probably the main strain of criticism of Hollinghurst is that his characters aren't likeable enough, that if there is feeling in his novels, then it's too deeply suppressed. For some, there isn't a tension between the visceral sex and the highly developed perceptions, merely a sense that both lack emotional heft. 'If he does write a book that gives you someone really to care about, writers will have to make a bonfire of their nibs,' Adam Mars-Jones says.

But those who know him insist that underneath the erudition and the witty, high-camp banter, he is emotional; indeed, that he's a person of particularly deep emotion. 'He's a loving person,' says Alan Jenkins. 'He's very loyal. He's not promiscuous: he falls in love with people and he's had terrible heartbreaks and unhappiness. Love and affection is very central in his life and I'm sure he'd like that to figure in his domestic life.'

Andrew Motion considers that Hollinghurst has 'a great capacity for joy and happiness', but doesn't believe that his intensely romantic nature naturally or inevitably leads to desire for completion by another person. 'I asked him once whether he was lonely and he said he has never been lonely. His sense of self is very centred.'

It is probably the case that with his impeccably organised flat in Hampstead, his views over the Heath, his walks, his large and varied circle of friends, Hollinghurst has, as Motion believes, life set up pretty much as he wants it; and yet, the books are full of yearning.

He writes about a gay world of uncertain possibilities and tenuous connections, 'where happiness can depend on the glance of a stranger, caught and held.' He is, as Stephen Pickles notes in a more general context, 'fascinated by what's over the wall, a secret garden thing'.

Pickles compares Hollinghurst's writing to a Renaissance painting, 'where there's a tiny little jetty in the background. Everything is done so well, right up to the little corner where you needn't put anything. That ultimately accounts for the pleasure: the books are substantial, and they shimmer.' Andrew Motion says he 'can't think of anybody who writes better line-by-line: weighed, scrupulous, thrilling, and charged.'

Many people thought Hollinghurst should have won the Booker last time he was short listed; there were suspicions that the graphic descriptions of sex might have put off one or two of the judges.

This week, a decade on, might just be his moment.

ALAN HOLLINGHURST

DoB: 1954, Stroud, Gloucestershire

Education: Magdalen College, Oxford

Job: On the staff of the Times Literary Supplement, 1982 to 1995

Books: Confidential Chats with Boys , The Swimming-Pool Library , The Spell , The Line of Beauty among others